New World Datsuns...

Bets me man.

I took the other seal out with a dentist tool.

What I am asking is what is the measurement from that grease fitting to the end of the yoke on that 521 driveline, then I would ask what the measurement is from that same point to the end of the yoke on the 520 driveline with the 720 yoke?

uberkevin » Sun Oct 05, 2014 2:20 pm wrote:Okay..


Here's the 521 set up. We'll half.
The yoke isn't bolted on.
Wayno your asking for the measurements of THIS drive line bolted together yes?

I'll measure what's in the photo bolted together.

Then I'll measure the 520 DL with the 720 yoke on it.

Wayno. I don't have the other piece of the stock 521 DL are you asking me to measure the whole stock 521 two piece? Or is that the grease fitting after the carrier bearing?

uberkevin » Sun Oct 05, 2014 6:49 pm wrote:I'll measure what's in the photo bolted together.

Then I'll measure the 520 DL with the 720 yoke on it.

Wayno. I don't have the other piece of the stock 521 DL are you asking me to measure the whole stock 521 two piece? Or is that the grease fitting after the carrier bearing?

What I am trying to find out is which assembly is longer from that grease fitting on the "U" joint to the end of the yoke, if the 521 flange/yoke is longer, then if you put that on your 520 driveline, it will stick in the tranny farther.
You had that transmission apart, did you remove any bearings when you had it apart, specifically any bearing in the tail housing?

Didn't remove any bearings from the tail.
I did change a front bearing.

Wayno.
I did have the 520 drive line with the 521 yoke/u joint flange on.
This made my driveline to short when bolted to the rear diff flange. The 520 driveline with the 521 yoke is much shorter then with the 720 yoke..
If I remember you told me that the 720 yoke was longer. Hmm maybe not you. Idk. But! I never tried the stock 521 drive line set up with carrier bearing and such. I need to get the rear section of the drive line to try.

If it is shorter, then that answers my question, I was thinking with the flange added in there that it might be longer.
I am always thinking about other ways to do stuff.
It's kinda baffling, others have done this same thing without issues.

Yeah I'm pretty damn sure jrock has this same fucking set up.
520 drive line 720 yoke. 720 short trans.
He truck is much! Lower how ever. I don't know if he did anything other then what he posted. I messaged him asking if he had to do in trouble shooting.

Heres what I'm thinking.
I'll measure the length needed. WITH the 521 yoke in the trans.
Then measure the 520 DL from 720 yoke to the flange end of the drive line..

This said! I measure from the end of the transmission yoke '521 yoke/with plug' to the rear diff flange just as it sounds right???

How far away from the rear flange was the rearend pinion flange with the driveline pushed all the way into the transmission?

I think about an inch and a half. But!
I think the rear end was in the air at that time.

So ill check that tomorrow while it's on the ground.

With the 521 flange on the 520 drive line
here how much it was off.

So i changed that set up above to what I have now 520 drive line with 720 yoke.

So there is less space between them with the 720 yoke on the 520 driveline?

wayno » Sun Oct 05, 2014 8:23 pm wrote:So there is less space between them with the 720 yoke on the 520 driveline?

So i made up the gap with the 720 yoke being put on but didn't take in to account how much it 'the 720 yoke' would be pulled out when the ujoint part of the 720 yoke was put on the 520 drive line. If you understand.

So i made up that gap above but once I changed the yoke it didn't matter cuz that pulled the new yoke out I guess to much.

uberkevin » Sun Oct 05, 2014 9:30 pm wrote:So i made up that gap above but once I changed the yoke it didn't matter cuz that pulled the new yoke out I guess to much.

We are back to this again, if the 720 yoke is longer than the 521 yoke, how can that gap be larger?
Unless the flange assembly makes the 521 yoke assembly longer from that grease fitting to the end of the yoke, as the 720 yoke doesn't have the flange assembly.
Having the driveline yoke pulled out of the transmission about an inch is not enough to cause an issue, at least I don't think it is, as it has to have room to move in and out a little when the truck is loaded or when it hits big bumps.
I don't have this issue because I have a carrier bearing on everything Datsun truck I own except for the 320s, so I may not have a clue what I am talking about.
One thing to keep in mind, Jrocks truck is always broken, so it's hard to say if he was having seal issues on his truck.

I didn't think pulling the driveline out an inch or so would be a problem buuuut it seems so.

I'm thinking the red area in this picture is stopping the driveline from going to far in when I push my current drive line in all the way leaving an inch from the rear flange.

uberkevin » Sun Oct 05, 2014 9:59 pm wrote:I didn't think pulling the driveline out an inch or so would be a problem buuuut it seems so.

If the truck don't vibrate when you get it up to speed, it's something else, bad yoke, wrong seal, something has a crack like the tail housing, the rear bearing in the transmission should be strong enough to keep the spline shaft from moving around or sagging in the housing and causing a gap for the fluid to come out of.
There is something else going on here.

Basically, I didnt read above, and reject all above as reasons, and I think wayno is on to something...

That tail of the tranny is chewed up. Something there is amiss. The seal should just work. I think it would have more to do with a gap or something, or a crack. Have you actually pin pointed where the fluid is actually coming from? Between the seal and yoke? Seal and transmission? Somewhere else right at the back?

If its not vibrating, and the shaft even goes in a little it shouldnt leak. The seal should be touching the yoke regardless of how far it is or isnt. Maybe there are 2 diameter seals? If you have a pair of calipers (measuring tool), I would take a measurement of the 2 yokes and see how close they are.

Or be a chevy guy and just pack RTV in there... but really maybe some Sil-Glyde would do wonders for keeping the oil in...

My thinking is something has to be wrong with the 720 yoke.

Remember I put the 521 yoke in the rear of the transmission and spun the bitch, now I didn't do it long but I'll do this again today. Yesterday when I did this nothing dripped out.

As far as finding the leak.
Well I can't really see the rear seal after I put the drive line in because of the 720 yoke, it has that 4 skin sleeve around it, the area in red I think is feeling up with oil 'maybe small amount' and as I spin the motor it builds up and comes spitting out, after about minute of driving there's a puddle of gear oil under the drive line.. then after about 2 minutes it starts to slow down and begins to build up on the shifting thing above the rear seal down onto the drive line.

SO ill get my ass out there and see again if the 521 yoke leaks while spinning. And do this longer then I did yesterday.